Radar is an electronic device for the detection and location of objects. One of the most common types of radar, pulse radar, operates by transmitting pulses of electromagnetic energy and then detecting echoes caused by reflections from a remotely located object ("target"). By measuring the time between the transmission of the pulse and the detection of the echo, it is possible to determine the distance of the object from the radar transmitter. This information, when coupled with the orientation of the antenna which received the echo, can be used to determine the location of the object. The relative position of the object can then be displayed on a video terminal or other appropriate device.
Although the underlying principles of pulse radar are conceptually simple, actual systems require relatively complicated equipment involving sophisticated circuitry for radar signal processing. As with all technical equipment, and especially complicated equipment, training is a crucial part of preparing personnel to operate and maintain radar systems competently. It is preferable to provide such training on an individualized basis, in the field, with actual radar equipment and with real targets. More realistically, field training on actual radar equipment and with real targets is frequently not possible and classroom training is the only alternative. Still, to provide the most effective training in the classroom environment, it is important to offer individualized training and to simulate real life conditions as closely as possible.
Conventional pulse radar systems, however, have not been well-suited for classroom training. First of all, duplicating a full-scale conventional pulse radar system for teaching purposes is expensive. Secondly, full-scale radar systems are incapable of operation at the close ranges and high resolutions compatible with the dimensions of a normal classroom, so that even when such systems are available, a student must observe targets which are located some distance away from the classroom. As a practical matter then, the student using such a radar has no control over the targets observed. He cannot easily arrange a configuration of targets to see how that affects the radar pattern; he cannot alter the orientation of the target to observe how that affects the radar signal; and he cannot easily compare selected target cross-sections with each other. In short, the versatility and value of a full-scale conventional radar as a classroom learning tool is quite limited.
Finally, a conventional pulse radar transmits high energy levels which are hazardous to humans. Predictably, the level of hazard is magnified in proportion to the number of systems operating at a given location. Consequently, to avoid risking injury to human life, it is essential to severely limit the number of systems concurrently operating in the classroom. With this limitation, individualized, hands-on training using conventional pulse radar becomes impractical.
One alternative to using a conventional pulse radar for training purposes is a computer simulator. Given the low cost of microcomputers, such systems are relatively inexpensive. Target placement and movement are merely programming options that are well within the control of the student. And since such systems transmit no actual radar signals, their use does not present a safety hazard. On the other hand, computer simulators sometimes do not offer the desired realism. Although it is possible to improve the sense of realism by using a more powerful computer, the system then becomes economically unattractive.
A desirable alternative would be to use a actual radar system that has a range and resolution within the scale of a typical training laboratory. With such a system, the student could observe scaled models of targets which are placed within and moved about the laboratory. Such a system would offer the realism of a conventional radar system, as well as the advantages of providing complete control over the selection and placement of targets. Moreover, since it is short range, the transmitted energy would be substantially less than for conventional pulse radar; therefore, the hazards normally associated with conventional high power pulse radars would be nonexistent.
In spite of the desirability of a short range, high resolution radar for training purposes, such systems historically have not been available due to significant technological and financial barriers to their development. Among the more serious problems have been those associated with the generation of the radar signal and the complexity and cost of the high bandwidth circuitry required in the receiver. To begin with, short range detection on the scale of a few meters with a resolution of a few centimeters requires sub-nanosecond duration pulses of radar frequency (RF) energy with corresponding RF bandwidths in the gigahertz (GHz) range. Conventional radar pulse modulators are not, in the present state of the art, adapted to the generation of such short RF pulse widths.
Even when such radars are adapted to process sub-nanosecond RF pulses, the required circuits are characteristically complex and very expensive. For example, such radar systems achieve target location for short duration RF pulses only through the use of specialized detection and range gating circuits; they do not permit actual sampling and recreation of the fine shape of the RF pulse. Because recreation and display of the fine pulse shape is sometimes critical in understanding how a radar operates, such systems are often not adequate for teaching how a conventional radar operates.
Therefore, it is a general object of this invention to provide a short range, high resolution pulse radar system.
Another object of this invention is to provide a short range, pulse radar system which is economically viable as an instructional device for individualized training of radar operators and other technical, engineering and scientific staff in a laboratory environment.
Yet another object of this invention is to provide a radar training system which can be used to detect and accurately locate model targets in a training laboratory environment.
A further object of this invention is to provide such a radar system which accurately reproduces the operation of a conventional long range, low resolution radar used in the field.
Other objects either are stated in the following description or will become evident in view of the description of the preferred embodiment.